For example, in the nailing machine using the compressed air as a power source, a hollow-cylindrical driving cylinder is arranged within a housing constituting a nailing machine body and a driving piston integrally coupled with a driver for striking the nail is slidably accommodated within the driving cylinder. By impactively driving the driving piston downward from an upper dead center position within the driving cylinder in such a manner that the compressed air is introduced into the driving cylinder, the nail is driven into the work by the driver coupled with the driving piston. Beneath the housing, a nose is integrally formed which serves to guide the driver slidably accommodated and forms a discharge port for guiding the nail to be driven by the driver. The driver coupled with the driving piston, which is accommodated in the discharge port, is slidably guided. By driving the driving piston, the driver coupled with the driving piston is impactively operated in the discharge port so as to strike the nail supplied into the discharge port, thereby driving the nail into the work from the discharge port.
As described above, in the power-driven nailing machine, which is provided with an impact mechanism for impactively driving the driver for striking the nail by the pressure of compressed air or combustion gas and serves to strike the nail by the driver driven through this impact mechanism so as to be driven into the work such as wood, concrete or steel plate, in reaction to impactively driving the driving piston coupled with the above driver within the driving cylinder, a reaction force in a direction opposite to the acting direction of the driving piston is generated within the housing accommodating the impact mechanism. By this reacting phenomenon, the nose integrally coupled with the housing will move upwards. As a result, the nail discharge port leaves the face of the work. Thus, the driver striking the head of the nail strays off from the nail head so that the face of the work is struck and damaged, thus generating a driver mark.
In order that the discharge port for driving/guiding the nail is not isolated from the face of the work even when the nailing machine body has moved upwards from the work because of the reaction during nail striking, the nailing machine has been proposed in which as shown in FIG. 7, a contact nose 31 is slidably provided at a leading end of a nose body 30 and the nail driven out from a discharge port 32 of the nose body 30 is vertically guided by a leading end discharge port 33 formed in the contact nose 31 thereby to drive the nail into the work (see JP-A-2002-337066). In this conventional nailing machine, the contact nose 31 giving the leading end discharge port 33 is held by the nose body 30 so that it is urged slidably along the discharge port 32 of the nose body 30 and protrusively forward from the nose body 30 in its leading end. So, even when the nose body 30 moves upward from the face of the work by reaction, the contact status between the contact nose 31 and the face of the work is kept, thereby preventing occurrence of the driver mark.
Meanwhile, in the nailing machine provided with the contact nose 31, in a state where the contact nose 31 has moved upward against the nose body 30 in order to actuate the nailing machine, the discharge port 32 of the nose body 30 and the discharge port of the contact nose 31 are formed to be continuous to each other. In this case, if the nose body 30 moves upwards by reaction in nail driving, between the leading end discharge port 33 of the contact nose 31 and the discharge port 32 of the nose body 30, a gap 34 having a larger inner diameter than that of these discharge ports will be generated. However, at the upper portion of the leading end discharge port 33 of the contact nose 31, a tapered guide face 35 is formed so that even when the gap 34 is generated as described above, the nail driven from the discharge port 32 of the nose body 30 can be smoothly guided into the leading end discharge port 33 of the contact nose 31.
Generally, the inner diameter of the discharge port of the nailing machine is formed to be slightly larger than that of the head of the nail. So the head H of the nail guided by the discharge port is located at the center of the discharge port whereas the leading end P thereof is placed in a free state within the discharge port. As a result, the nail with a shaft slanted may be driven. Since a concrete nail or steel plate nail N has a relatively short shaft, the slanting angle of the nail shaft may be large within the discharge port. Therefore, for the concrete nail, for example, in order to prevent the nail from slanting within the discharge port, a ring-shaped foot guide G is mounted at the leading end portion of the nail shaft so that the outer peripheral edge of the food guide G is engaged with the inner wall of the discharge port 32. Thus, the leading end P of the nail shaft is arranged at the center of the discharge port 32 so that the nail shaft is kept perpendicularly to the face of the work.
Where the concrete nail or steel plate nail with the foot guide G mounted at the leading end of its shaft as described above is driven through the above conventional contact nose 31, as seen from FIG. 7, the leading end P of the nail shaft is located at the center of the leading end discharge port 33 in such a manner that the foot guide G is fit on the inner periphery of the leading end discharge port 33 of the contact nose 31, whereas the head H thereof may be placed in a gap 34 having a larger inner diameter formed between the lower end of the nose body moved upward owing to reaction and the upper area of the leading end discharge port 33 of the contact nose 31. As a result, the nail N may be driven from the contact nose 31, while the head H of the nail N is deviated from the central position of the discharge port so that with the nail shaft being slanted.